Upon receiving signals to be transmitted, conventional wireless communication devices that conduct communication with wireless signals convert, to modulation signals, signals to be transmitted received as local signals and then transmit the converted signals by using a quadrature modulation circuit to perform quadrature modulation on the local signals that become carrier waves. Modulation systems for performing quadrature modulation use quadrature phase shift keying (QPSK) or quadrature amplitude modulation (QAM) and the like. However, a DC offset is produced as noise due to imperfections of the elements in the abovementioned quadrature modulation circuit and the DC offset is added to the modulation signals.
Accordingly, Japanese Laid-open Patent Publication No. 10-079693 describes a technique for calculating a DC offset of a quadrature modulation circuit, for example, by providing a feedback circuit that provides feedback by using a quadrature demodulation circuit to perform quadrature demodulation on modulation signals, and by switching inputs and non-inputs of the modulation signals to the feedback circuit. Moreover, Japanese Laid-open Patent Publication No. 2002-077285 describes a technique for calculating a DC offset of a quadrature modulation circuit by using, for example, a frequency converting circuit to convert modulation signals to IF signals and then by using an ADC to perform digital conversion to provide feedback.